In recent years, a motor-powered vehicle has been in practical use. The motor-powered vehicle is a vehicle capable of running with a motor driven by electric power supplied from a battery. An example of the motor-powered vehicle includes a hybrid vehicle (HV), an electric vehicle (EV), and a fuel cell vehicle (FCV). In a drive system employed in such a motor-powered vehicle, a main relay is interposed between a battery and a power converter. In such a drive system, there is a need to detect contact welding in the main relay and to produce an alarm when the contact welding is detected.
JP-A-2012-5174 corresponding to WO2011-158088 discloses a technique for detecting contact welding in a structure where multiple batteries are connected in series, and a main relay is connected in series to each of positive and negative terminals of each battery. In JP-A-2012-5174, an electronic control unit (ECU) turns OFF one main relay while turning ON the other main relays in order to detect whether the one main relay suffers from contact welding. The one main relay is hereinafter referred to as the “target main relay”. If the target main relay suffers from contact welding, an input voltage to a power converter increases. The ECU detects whether each main relay suffers from contact welding by in turn changing the target main relay.
In some cases, multiple batteries having the same nominal voltage and capacity are connected in parallel to increase the total battery capacity. In such a case, it is impossible to detect whether the target main relay suffers from contact welding by turning OFF the target main relay while turning ON the other main relays in a manner as described in JP-A-2012-5174. Therefore, if there is a possibility that any one of the main relays suffers from contact welding, all the main relays need to be replaced with new ones.